The present invention relates to a device and method for testing batteries, light bulbs, and fuses. More specifically, the invention relates to a device and method for testing batteries, light bulbs and fuses which provides accurate, easy-to-read results as to the condition of the item being tested, which is relatively simple to use, and which is ergonomic in design and operation.
In particular, this invention relates to battery testers as commonly used for testing dry cell batteries. The term battery may be used collectively in the present context to include reference to single as well as multiple cells. The widespread use of batteries in consumer appliances, such as portable AM/FM radios, CD players, MP3 players, watches, calculators, hearing aids, PDA's, toys, games, etc., has given rise to a significant demand for devices for testing them. Furthermore, it is noted that some of the batteries that need to be tested, such as the small “button” cells which are increasingly being used for powering more and more electronic devices, can pose particular problems, given their small size, for the elderly to manipulate. This can be particularly distressing given that these batteries are of the type that are generally used in hearing aids.
In addition, many bulbs and fuses are likewise used in everyday household and automotive applications. Just as it is not possible to determine the condition of a battery by looking at it, it is likewise impossible (in many cases) to determine the condition of a bulb or fuse merely by looking at it. Small bulbs, such as those used in Christmas light strings, are often colored and use small filaments, so it is not easy to know if the filament is broken or burned out by observation. As another example, it is difficult to determine if a small Halogen “pin” bulb is burned out or not because the filaments inside these bulbs are typically difficult to observe through the relatively thick glass of the bulb. In addition, some small automotive fuses are hard to “read” by observation. These examples underscore the need for a simple bulb and fuse tester.
With respect to the testing of a bulb or fuse, it is noted that both of these devices are essentially “closed circuit” devices. A bulb has a very thin wire called a filament inside a protective glass shell. The filament gets very hot when current is passed through it. When it gets hot, it glows to produce visible light. When the filament burns out or is broken, then of course current cannot pass through the filament and therefore it will not produce light. A fuse works in a similar manner, but with the difference that the wire inside a fuse is relatively large or thick and is sized to carry a certain amount of high current before it melts and opens the circuit, interrupting the flow of current. A fuse is not intended to glow and produce light. Instead, the material used in a fuse is designed to melt when the current flowing in a circuit surpasses the design limit of the fuse wire, at which time it interrupts the current flow and causes an open circuit. The fuse thus sacrifices itself to protect other more sensitive and expensive components in the circuit, including the circuit wiring.
To test a bulb or fuse, therefore, a circuit is necessary which is able to test the “continuity” of the device. To do so, the circuit must have a source of current. Therefore, a “continuity” tester is normally designed to use an internal voltage source, usually some sort of battery, that may be used to cause a small current to flow through the bulb or fuse when it is placed in the test circuit. In addition to the battery, a galvanometer movement (a small meter with a pointer that is deflected when current flows through the meter) is also normally used in the test circuit to measure the amount of current passing through the bulb or fuse. If the bulb or fuse is acceptable for use, then the current passing through the bulb or fuse causes the galvanometer to deflect (or light up a light on the meter) to represent this fact. A Light Emitting Diode (LED) can be used as the light in such circumstance to indicate the “good” or “bad” status of the bulb or fuse if desired.
As mentioned above, it is also frequently desired to have a tester which accurately tests the condition of a battery. Such accurate testing can generally not be accomplished using a simple open circuit-type terminal voltage tester, instead requiring a load-based tester. Load-based testers are considered an improvement over less-expensive open circuit testers in that load-based testers are designed to measure the closed circuit battery terminal voltage under a load. In contrast, most inexpensive open circuit battery testers merely measure the open circuit battery terminal voltage with no load. And while such testers do not generally require the use of a complicated electronic circuit, integrated circuit (IC), or a microprocessor, thereby making them relatively inexpensive to design and make, the results obtained using such testers are not nearly as accurate or consistent as the results obtained using a load-based battery tester.
More specifically, open circuit-type testers are relatively limited in value because they do not test a battery under a realistic “load” condition. Under a load, the terminal voltage of a battery will decrease to a much greater extent than if no load is applied. The state of the battery terminal voltage under load will provide a much more meaningful measure of how much useful life is remaining in a battery. However, as noted above, load testers, because they must apply a given load that is dependent on the properties of the battery being tested, normally require more sophisticated electronic circuits than open circuit testers.
In practice, a load-based battery tester places a resistive load across the terminals of the battery to be tested and then measures the drop in terminal voltage as a result of the applied load. The remaining life of the battery is then a measure of the relative drop in terminal voltage under the applied load (closed circuit voltage). The results are calculated on the basis that every battery has a milliampere hour (mAh) rating from the manufacturer. A fully charged battery exhibits a maximum terminal voltage and a maximum mAh capacity. As the battery is used and becomes discharged, the terminal voltage begins to drop. At some point, called the cutoff voltage, the battery can no longer provide sufficient electrical energy to power an electronic device. Thus, the remaining useful life of a battery can be determined by measuring the terminal voltage under a given load. This voltage will begin at a maximum voltage (fully charged) and end at the cutoff voltage where the battery is “dead” or fully discharged. At closed circuit voltages in between these extremes, the percent of battery life remaining can be scaled and appropriately indicated by a meter or lights.
More specifically, the circuit in a load tester may be designed to cause a meter to deflect a given amount or cause small Light Emitting Diodes (LEDs) to illuminate at certain voltage thresholds designed into the circuit. If there is virtually no voltage drop under a test load, the battery should read as “good”. If the battery drops to the cutoff voltage specified by the battery manufacturer, then the tester should indicate that the battery is “bad” and should be changed. Thresholds in between these extremes can be calibrated to show various levels of remaining battery life.
In addition to testing battery life, as noted above, it is also sometimes desired to have a testing device that is capable of testing the general condition of light bulbs and/or fuses.
Accordingly, there is a need for compact, economical testers capable of simply and easily testing a range of batteries varying size and/or voltages, light bulbs, and/or fuses and providing and accurate indication of condition of the tested device to a user thereof.